Pencil lead



Patented Apr. 15, 1941 PENCIL:

Isidor Chesler, Oceanport, N. 3., aesignor to Eagle Pencil Company 1110., New York, N. Y.,' a corporation of Delaware No Drawing. Application December 30, i939, Serial No. 811,944

Claims.

The present invention relates to a pencil lead which makes a mark of conventional appearance, capable of being readily identified as havvolatile solvent such for instance as alcohol. After such impregnationfthe leads are drained and then dried by tumbling in sawdust. Thereupon, the alcohol solvent would be. evaporated particular application is accordingly intended to bility, uniformity, and smooth writing of predetermined hardness or softness.

Another objectis to provide a ,lead oi the above type, the cost of production of which is but slightly higher than that of ordinary leads of corresponding quality and which is not subject to deterioration in anyrespect even long after it has been fabricated.

Another object is to provide a lead of the above type which, despite its specialized properties, has

no ingredients therein apt to impair or destroy the card or paper on which the pencil is used and which has no toxic constituent apt to cause injury by contactwith the fingers or tongue of the user.

According to the invention, the lead prepared of one of the usual mixtures of graphite and clay, fired according to conventional practice, has incorporated in the minute interstices thus formed therein and prior to wax or oil impregnation thereof, same color agency either in the form of a suitable soluble dye, or of a dye intermediate or an indicator that gives a color reaction upon appropriate treatment, so that when a pencil marking on the sheet is suitably moistened, a tell-tale coloration willappear, where an ordinary lead pencil mark would show no change upon corresponding treatment.

It is preferred to use as the color medium a dye, such as rhodamine, eosine, methylene blue or methyl violet. A solution of the dye will readily penetrate into the interstices of the fired lead. It is advantageous to impregnate the leads with a solution of such dye. in a relatively by placing the leads in an oven"at a suitable temperature for a suflicient period of time. As I a consequence, the dry dye will remain as a deposit on the walls'of the labyrinthine interstices or pores. The leads are thereupon preferably impregnated with further dye in a non-volatile hygroscopic solution, then drained, rinsed and dried. Finally the leads are desirably impregnated in oil or wax and tumbled in sawdust.

In one specific way of carrying out the invention, the leads prior to wax or oil impregnation thereof, are immersed in a bath of a volatile carrier such as ethyl alcohol containing five per cent by weight of a dye such as rhodamine. To insure solution of the dye, the bath is first heated and the immersion may be at room temperature,

desirably for about three hours. The leads are then removed from the bath, drained, dried in sawdust and spread on a screen overnight at room temperature to allow complete evaporation of the alcohol from the leads.

After the leads have thus been dried, theyare immersed in a second bath including preferably a non-volatile carrier comprising a solution of a hygroscopic ,polyhydric alcoholsuch as glycerin with associated water, an ionogen such as boric acid and a dye such as rhodamine in suitable proportions. second bath are in the proportion of 200 c. c. of glycerine to grams of boric acid and 7.5 grams of rhodamine. The bath is kept at a temperature of about 120 degrees C. and the leads remain immersed therein for about three hours. Thereafter, the leads are removed and drained for not more than a couple of minutes and thereupon quickly rinsed in cold water and dried in sawdust.

Finally the leads are impregnated with oil or grease according to usual practice, but it is preferred for the particluar p p se in hand to immerse them for about fifteen minutes in tallow kept at degrees C'., the excess being thereupon cleaned off by tumbling in sawdust.

The lead of the specifications set forth will maintain its'efiicacy for long periods of time, by

, reason of the fact that the hygroscopic glycerin ingredient thereof retains sufflcient water to maintain the boric acid and the dye in solution therein at all times and the tallow acts to .a large extent as a seal to keep the water retained by the glycerine from escaping with rise in tem- Desirably, the ingredients of-the and of the desired degree of hardness.

perature and to preclude excess water from an tering under conditions of excessive humidity.

Even though the mark made by the lead is not fresh, it will have all the propertiesrequired for the present purpose. The mark will be black The glycerin-water ingredient of the mark will have in solution therein'both the boric acid and the dye and the water is kept in situ by the tallow, so that the electrical resistance of themark is and remains low as required for the particular specific purpose for which the lead is adapted.

Lead prepared in the manner set forth will give a black mark indistinguishable to the eye from that made by ordinary lead pencils of corresponding grade and quality. To test the mark in order to verify whether it has been made with the specialized pencil, a drop of alcohol need merely be applied to a portion of the mark. It

immediately dissolves some 01' the rhodamine and leaves a halo about the mark as the drop spreads, giving the tell-tale indication. which is lacking when alcohol is applied to a mark made by an ordinary panel]. 1

While ethyl alcohol pure or denatured is preferred as the solvent, it is obvious that other solvents such as methyl alcohol may be used, but by reason of the toxic character of some of such other solvents, the ethyl alcohol is to be preferred.

Another way of producing substantially the Instead of alcohol soluble dyes such as those above suggested, an oil soluble dye might be used, such as double xylidine compound for red. The useof such oil soluble dye has the advantage that it could be admixed with the waxes or oils employed and the mixture could be applied in a single impregnation. With such dyes the paper would be moistened at a markedarea with an oil solvent, preferably a hydrocarbon such for instance as benzine, in order to test for the tell-tale indication. I

Instead ofa dye, a suitable dye intermediate could be used, and a marked area would be moistened with an appropriate the'tell-tale trace.

Another alternative is an indicator such as phenolpthalein, desirably in a glycerin carrier, preferably with aboutjten per cent of the indideveloper to test for article and method and many apparently widely different embodiments of this invention could be made without departing from the scope of the claims, ,it is intended that all matter contained in the above description shall be interpreted as the pores thereof, ineffective to alter the black coloration of the mark made by the lead and upon the application of a suitable liquid to yield a tell-tale indication in the form of a halo of contrasting color.

2. A pencil lead of 'fired graphite and clay having a colored ingredient lodged in the pores thereof, ineffective to alter the black coloration of the mark made by the lead and upon the application to such mark of a suitable solvent for the colored ingredient to yield a tell-tale trace in the-form'of a halo' of contrasting color.

3. A pencil lead of fired graphite and clay having dye lodged in relatively dry condition in the pores thereof, ineffective to alter the black coloration of the mark made by the lead and upon the application to such mark of a solvent for the dye yielding a tell-tale indication in the form of a halo of contrasting color.

4. A pencil lead of fired graphite and clay having deposited in the pores thereof,- a dye of the group which consists of eosine, rhodamine, methylene blue and methyl violet, said dye being ineffective to alter the black coloration of the mark made by the lead and upon the application to the mark of a drop of dye solvent yielding a tell-tale indication in the form of a halo of contrasting color.

5. A pencil lead of fired graphite and clay having the pores thereof substantially filled with cator dispersed therein. The leads would be 1111- I mersed in the glycerin mixture for about fifteen minutes at a temperature of about 285 degrees C. and after removal from the mixture would be rinsed in cold water for fifteen minutes and thereupon dried in sawdust. For verifying the identity of a mark made with a lead thus impregnated a marked area would preferably be wetted with a weak alkaline solution to test for a tell-tale red mark. I

Where the leads are to be used with a statistical machine of the type that depends on low electrical resistance of the pencil mark, it is desirable to use in the lead a graphite of relatively low resistance.

The invention is not limited 'in its application As many changes could be made in the above a waxy substance and an oil soluble dye ineffective to alter the black coloration of the mark made by the lead and soluble upon the application to such mark of suitable solvent, to yield a tell-tale indication in the form of a halo of contrasting color.

6. A pencil lead of fired graphite and clay having the interstices thereof impregnated with a non-volatile liquid ingredient of hygroscopic character having in solution therein an ionogen and a dye.

'7. A pencil lead of fired graphite and clay having the interstices thereof impregnated with a polyhydric alcohol of hygroscopic character having in solution therein an ionogen and a dye soluble in the polyhydric alcohol.

8. A pencil lead of fired graphite and clay having the interstices thereof filled with water carrying glycerin, boric acid, rhodamine dye and tallow.

9. A pencil lead of fired graphite and clay having the interstices. thereof impregnated with a chemical indicator in a non-aqueous carrier.-

10. A pencil lead of fired graphite and clay having the interstices thereof impregnated with phenolpthalein in glycerin.

11. The method of prepering a pencil lead the mark of which will show a contrasting color when treated. with appropriate liquid, which comprises impregnating the fired lead with a hygroscopic non-volatile liquid carrier having an ionogen and a dye in solution therein.

12. The method of preparing a pencil lead the mark of which will show a contrasting color aaaam a when treated with appropriate liquid, which comprises impregnating the tired lead with a volatile carnier having coloring matter distributed therein, evaporating the carrier and thereupon impregnating the lead with a non-volatile hygroscopic carrier having an ionogen and a dye in solution therein.

13. The method of preparing a pencil lead the mark of which will show a contrasting color when. treated with appropriate liquid, which l0 comprises impregnating the tired lead with glycerin having boric acid and a dye in solution therein.

14. The method of preparing a pencil lead the I mark of which will show a contrasting color when treated with appropriate liquid; which comprises impregnatingthe fired lead with a volatile carrier having dye in solution therein,

evaporating the carnier therefrom, then impregnating the lead with anon-volatile hygroscopic carrier having an ionogen and dye dissolved therein and finally impregnating the lead in an oleaginous bath.

15. The method recited in claim 14 in which the non-volatile hygroscopic carrier is glycerin v and the ionogen is boric acid.

ISIDOR CHESLER. 

